1. Field of the Invention
The present invention relates to a feed regulator of a sewing machine which can change a seam length of a cloth at the time of stitching operation.
It is hitherto known that a sewing machine is provided with a reverse stitching mechanism as a conventional cloth feed regulator of the sewing machine (hereinafter referred to as feed regulator). The reverse stitching mechanism stitches the cloth partly as the feeding direction of the cloth to be stitched (hereinafter referred to as stitching cloth) is reversed for preventing fraying of a thread at the portion where the cloth is stitched first and last. The conventional reversing stitching is, in the reverse stitching mechanism as illustrated in FIG. 5, performed by an operator by stepping on a reverse stitching lever 101, thereby turning a feed regulating cam 102 so that an operating direction of a feed dog 103 is switched over. In an automatic reverse stitching mechanism, the feed regulating cam 102 is turned by operating a button, not shown. Designated at 104 is a feed regulating stud for controlling an inclining position of the feed regulating cam 102.
Seam length of the stitching cloth made by the conventional reverse stitching mechanism can not be varied since it is determined by a shape of a cam surface of the feed regulating cam 102 and is generally set to be the same as the seam length when the cloth is stitched by a forwarding stitching operation.
However, the cloth feed regulator of the sewing machine provided with the conventional reverse stitching mechanism has a single reverse stitching mechanism for performing the reverse stitching operation so that the seam length in the reverse stitching operation is not varied. As a result, the reverse stitching operation can be performed at the predetermined single seam length but cannot be performed at a seam length combining the predetermined single seam length with a seam length which is different from the predetermined single seam length. Although the operator can regulate a step rate of the feed reversing lever to keep the step position to the middle position in the reverse stitching mechanism provided with the reverse stitching lever, thereby performing the reverse stitching operation in the different seam length, the step rate is unstable and the operator must be experienced to obtain uniform seam pitches or lengths (hereinafter referred to as seam length).
For example, when stitching dart portions at a stitching starting position of the cloth BTS and stitching end position BTE of the cloth to prevent swelling of a stitching cloth 105 in FIG. 6, if the operator performs the reverse stitching while stepping fully on the reverse stitching lever, the stitching cloth is liable to swell. To prevent such swelling, the cloth is stitched at short seam length ST at the both ends BTS and BTE while the stepping rate of the reverse stitching lever is kept at the middle position as illustrated in FIG. 7.
In case of stitching a fastener on the cloth as illustrated in FIG. 8, if the short side S of the fastener is stitched at the same seam length as the long side L thereof, the stitching strength thereof is weak at the short side S. Accordingly, the fastener is repeatedly stitched as denoted BS in FIG. 8. As a result, it is necessary to step the reverse stitching lever frequently, which creates a troublesome operation.
The present invention is made to overcome the drawbacks of the conventional cloth feed regulating mechanism.
A feed regulator of a sewing machine according to a first aspect of the present invention comprises a first driving means for swingably driving a feed regulating table by way of a link mechanism and a feed dog for switching the feed operating direction. The feed regulator of a sewing machine further comprises a link member which is disposed so as not to hinder the operation of the link mechanism and has a slit, one side surface of which can retain a projection of the link mechanism. A second driving means imputs motion to the link member in the direction to move the link mechanism while said one side surface of the link member retains the projection of the link mechanism. The amount of operation of the link mechanism by the second driving means is set to be less than that by the first driving means.
A feed regulator of a sewing machine according to a second aspect of the present invention comprises a first driving means for swingably driving a feed regulating table by way of a link mechanism and a feed dog for switching the feed operating direction. The feed regulator of a sewing machine further comprises a feed regulating table supporting shaft which is incorporated in the feed regulating table and turnably supports the feed regulating table on a frame of the sewing machine. A feed regulating table supports a shaft crank which is fixed to the feed regulating table supporting shaft. An operating shaft crank which is turnably driven by the first driving means which is fixed to the frame of the sewing machine. A feed regulating table supporting shaft link is interposed between the feed regulating table supporting shaft crank and the operating shaft crank. A projection is defined in the feed regulating supporting shaft, the feed regulating table supporting shaft crank, or the operating shaft crank. A second driving means is fixed to the frame of the sewing machine. An eccentric cam is fixed to a forked crank which is turnable by the second driving means. The forked crank has a middle portion, which is turnably supported by the frame, one end defining forked portions for receiving the eccentric cam and another end connected to a link member. The link member has a slit one side of which is capable of retaining the projection thereby. The forked crank is turned for permitting one side surface of the link member to be retained by the projection so as to swing the feed regulating table supporting shaft.
A feed regulator of a sewing machine according to a third aspect of the present invention further comprises, in the feed regulator of a sewing machine of the second aspect of the present invention, first and second switches. The first switch issues a signal for operating the first driving means and the second switch issues a signal for operating the second driving means.
A feed regulator of a sewing machine according to a fourth aspect of the present invention further comprises, in the feed regulator of a sewing machine of the second aspect of the present invention, a selector switch for selecting the first driving means or the second driving means and a stepping pedal for operating the first or the second driving means.